A 62-year-old woman presents with a 12-hour history of severe right eye pain, blurred vision with halos around lights, nausea and vomiting. Examination shows vision 6/60, intraocular pressure 56 mmHg, corneal oedema, mid-dilated unreactive pupil and a shallow anterior chamber. After intravenous acetazolamide and topical timolol have been given, the next step is:

• A Immediate instillation of pilocarpine 4% every 15 minutes
• B Topical atropine to relieve ciliary spasm
• C Trabeculectomy as the definitive first procedure
• D Intravenous mannitol followed by peripheral laser iridotomy once the pressure falls ✓

Explanation

In an acute primary angle closure attack, osmotic agents such as IV mannitol are used when acetazolamide and topical agents fail to lower pressure adequately, because the ischemic sphincter does not respond to pilocarpine until the pressure falls below about 40 mmHg. Pilocarpine given immediately is therefore ineffective, and surgery is deferred until the eye is quiet enough for laser iridotomy.

Reference: Parsons' Diseases of the Eye, 23rd ed.

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Written and medically reviewed by the StethoPrep medical team.